Kinetic modeling and process simulation for ethanol steam reforming

Introduction The production of H2 from renewable sources is gaining growing attention. Among the various possibilities, the steam reforming of ethanol is in a quite mature development step, being object of various demonstrative projects [1]. Process simulation is a powerful tool in order to understand the real development possibilities for a technology. In order to do this, the process flowsheet should be drown and compared in different layouts, for proper optimization and comparative evaluation of efficiency and cost. In this work, we propose the optimization of an integrated cogeneration system, based on an ethanol steam reforming reactor, followed by a series of hydrogen purification reactors (two water gas shift units and a methanator) to achieve max 20 ppmv CO. This reformate is then fed to a fuel cell with residential cogeneration size (5 kW electrical + 5 kW thermal power). In order to size the reactors kinetic modelling has been carried out on originally derived data [2,3]. Besides the optimization of the thermal integration of the system, we checked the dependence of cogeneration efficiency on the key variables (reformer temperature, catalyst loading and water/ethanol ratio). The possibility to exploit diluted bioethanol solutions has been also explored as a way to improve the cost efficiency of the process. Materials and Methods Original kinetic data were collected for the steam reforming of ethanol on a home-prepared 10 wt% Ni / 9 wt% K2O-ZrO2 sample prepared by flame pyrolysis. Kinetic data have been collected according to a composite experimental design of experiments considering mono-and multivariate levels. The data have been elaborated according to a detailed microkinetic scheme, solved by using both Matlab and Aspen Plus. The kinetic model and the relative parameters were used for the simulation of the steam reforming reactor. Process simulation has been carried out by using the Aspen plus process simulator. Results and Discussion The possibility to use diluted bioethanol solutions as feed (e.g. 50 vol%, obtainable through a simple flash distillation) has been investigated in order to adopt a much less expensive feedstock. In this way the flowsheet has been designed so to use part of the reformate to feed a burner to thermally sustain the reformer. The most important variables affecting electrical and thermal efficiency were reformer temperature and the water/ethanol ratio. The amount of catalyst determined the ethanol conversion in the steam reformer. However the latter parameter could be effectively enhanced also by increasing the temperature or, much better, by increasing the water amount in the feed. The reformer temperature and of the water/ethanol ratio in the feed were tightly connected and ultimately governed the setting of the reformate splitting ratio, i.e. the amount of reformate used in the burner to sustain the steam reformer. This parameter was the most sensitive for the regulation of the plant. The overall power output of the cogeneration system was enhanced by using diluted bioethanol. By optimising the heat integration of the system we demonstrate that it is possible to effectively use diluted bioethanol streams. Figure 1. Sketch of the process flowsheet. Significance Process simulation and optimization has been carried out for hydrogen production by ethanol steam reforming. We demonstrate the possibility to use diluted bioethanol solutions (e.g. 50 vol%) for this process, representing a poorly expensive feedstock for the process. References 1. Rossetti, I., Biffi, C., Tantardini, G.F., Raimondi, M., Vitto, E., Alberti, D., Int. J. Hydrogen Energy, 37(12), 8499 (2012) 2. Compagnoni, M., Tripodi, A., Rossetti, I., Appl. Catal. B: Environmental, in press 3. Tripodi, A., Compagnoni, M., Rossetti, I., ChemCatChem, in press